This invention relates to a chemically unmodified hyaluronan product which has enormously high molecular weight and extremely high viscosity i.e. zero shear viscosity. This unique product is durable and at the same time viscoelastic, and perfectly compatible within the biocompatible materials, for instance, as a cartilage substitute and as a intervertebral disc. The invention also relates to a process for manufacturing of said product.
Hyaluronan (hyaluronic acid) is a naturally occurring polysaccharide which was first isolated in 1934 and 24 years later the structure of the molecule was totally defined. The first commerical product (Healon, trademark) was launched in 1980 within eye surgery, a product which is chemically unmodified. Since that time many similar product have been launched, some of them consist of only hyaluronan, with different molecular weight, from 0.5 to 8.0 million (Dalton) sterilized solution as described in the literature.
Most product are however, chemically modified hyaluronan, i.e. an extra chemical substance is added to the original hyaluronan molecule, to achieve higher viscoelastic properties, but it is always associated with risky side-effects. The cross-linked hyaluronan is known since 1963 (T. C. Laurent et al). A further drawback of cross-linked hyaluronan is the relatively short residence time in human tissues.
The chemical structure of hyaluronan is independent of origin in that hyaluronan is a linear polysaccharide without branching. The polysaccharide consists of a repeating disaccaharide unit of N-acetyl-D-glucosamino and glucuronate linked by xcex2(1xe2x86x923) and xcex2(1xe2x86x924) glycosidic bonds. It is well known that hyaluronan molecule in solution adopts a conformation of a stiffened random coil. Hyaluronan is produced by an enzyme complex in cell membranes. The enzymes produce hyaluronan from intracellular constituents, and the polysaccharide is directly extruded to the extracellular space.
The product of hyaluronan may be based on bacterial synthesis or on extraction from biological sources such as umbilical cord and rooster combs. The molecular weight of the isolated material depends, inter alia, on the quality of the raw material and the methods used for leaching, extraction, purification, sterilisation and the quality system. Strains of certain Streptococcus bacteria are capable of producing hyaluronan with molecular weights lower than leaching and extraction from rooster combs.
Hyaluronan produced by bacteria has to be cross-linked to achieve the higher molecular weight (i.e. zero shear viscosity) products required within the medical field.
To avoid the drawbacks with a chemically modified substance an unmodified hyaluronan product with high molelcular weight (i.e. zero shear viscosity) is infinitely preferable.
The present invention provides chemically unmodified hyaluronan with greatly improved molecular weight (i.e. zero shear viscosity) and with multiple applications within the medical field.
This inventin has been made possible through observing many previously unknown quality parameters plus the application of new technology with a combination of many steps from treatment of the naturally occurring raw material to the sterile end product. The process according to the invention is very rapid and takes at the most 1xc2xd day to perform.
The process for production of hyluronan products gives according to the invention sterile products with zero shear viscosity from 5 million to 30 billion mPa s, which is totally unique. Due to the incredibly high shear vicosity it is possible to create various biocompatible products to be used in human beings and animals.
According to the present invention, greatly improved molecular weights are obtained and with suitable concentration, a product with specific viscoelastic properties can be created. Within the molecular weight range of 9-25 million Daltons and the concentration range of 10-39 mg/ml zero shear viscosity (from 5 million to 30 billion mPa s) is achieved according to the invention with a shear rate of 0.001 Hz.
Viscoelastic behaviour
The connection between zero shear viscosity and molecular weight and concentration is well known, see the equation below.
Zero shear viscosity=5.3xc3x971026xc3x97(concentrationxc3x97Mr)3.643xe2x80x83xe2x80x83(unit=Pa s)
To produce viscoelastic substances with high zero shear viscosity, the only parameters that can be altered to create these products are molecular weight and concentration.
Note that, the parameter concentration is a strongly limiting factor. The colloid osmotic pressure of hyaluronan is of interest in conjunction with the use of hyaluronan substance in various body compartments. The colloid osmotic pressure is dependent on the number of molecular in solution and is thus a function of the number average molecular weight rather than the weight average molecular weight.
To arrive at an end product within the range of 9-25 million Dalton is extremely difficult, technically demanding and complicated. The patent application comprises a unique manufacturing system of sterile end products, whose vast medical significance is revolutionary for important clinical applications such as eye lenses, intervertebral discs, prostheses, etc
Hyaluronan (hyaluronic acid) has physical properties with a broad range of medical applications; in othopedics, rheumatology, ophthalmology, dermatology, plastic surgery, otology, rhinology, neurology, urology, cardiothoracic surgery, adhesion prevention.
Below a non-limiting example of the process of the invention will be described.
I. Process for the manufacturing of extremely high molecular weight hyaluronan
Raw material
As raw material especially roosters from the White Leghorn breed are used. They are genotypically and phenotypically selected within the molecular weight range of 10-50 million Daltons.
Extraction of water and salts and the reduction of microorganisms
Immediately after the combs are removed they are treated with 70% ethanol, proportion 1:5. Special equipment cleans the combs of biological impurities and this treatment is repeated 3-5 times with fresh ethanol. A diluted sodium phosphate solution can alternatively be added for the second step.
Pre-treatment of the combs
The combs are directly frozen to about xe2x88x9215 degrees Celsius sliced into extremely thin sections 0.001-0.1 mm thick, then rapidly frozen to xe2x88x9222 degrees Celsius in a freezing tunnel. Alternatively the combs can be ground into different particle sizes, instead of being sliced.
Leaching of hyaluronan under nitrogen atmosphere
In a diluted solution (0.5-2% NaCl solution) hyaluronan is leached from the material in up to seven steps, within nitrogen atmosphere. The leaching time varies from 3 minutes to 3 hours.
Removal of impurities under nitrogen atmosphere
The solution is treated with adsorptive media such as hydroxyapatite in one or several steps during gentle stirring and then filtrated.
Concentration of hyaluronan
The solution is concentrated for example through dialysis (PEG 3000)under vacuum conditions.
Packing and sterilisation of the hyaluronan product
With regard to molecular weight and concentration, different products are manufactured and packed into various types of dispensers. The product can be sterilised through radiation (16-28 kg Gray). Alternatively microwaves (10-300 W, 2450 Hz) or by autoclaving or sterile filtration of a diluted solution under acceptable conditions.
II. Medical application of the hyaluronan product
Based on the process of the invention four (A-D) separate intervals have been chosen for different medical applications with regard to rheological and chemical-physiological properties. Below an example in each category will be described.